Elon Musk's ideas are in the news right now, rockets with first stages that fly back to a soft landing under auto pilot. But you might be surprised to learn how many other ideas there are under active development, for low cost ways to get into orbit.

The British Skylon would fly directly into space from a reinforced airport, taking off like a plane, without need to discard anything (single stage to orbit). Then JP Aerospace plan airships to float up to 200,000 feet followed by transfer to a lighter than gossamer skinned, "orbital airship" that never lands, but can accelerate gradually through the near vacuum of the troposphere and above, to orbital velocities.

Other projects remain ideas, but worked out in some detail, and may be practical if funds become available. This includes, many ideas for single stage to orbit - tethers to pluck an airplane traveling at Mach 12 out of the atmosphere and boost it up to LEO at Mach 25 - lightweight craft propelled into space on a laser beam - space guns to fire materials such as water and fuel into orbit - super fast trains that accelerate to orbital speeds along Maglev tracks - and many more ideas.

Then you have the future dream of a space elevator made of exotic materials, which would let you go up in a lift to orbit from the Earth's equator - and more practical versions of this space elevator which could be built with present day technology on the Moon and on asteroids.

I thought it would be fun to look at some of these projects, first, and then I'll ask what our world will be like if we can fly into orbit as easily as we can cross an ocean in a plane. We have tens of thousands of planes in the air every day, and millions of flights a year.

That world may not be too far away, perhaps a couple of decades into the future, if any of these ideas pan out. Or it might be that none of them work and it's fifty years from now. Still many of those alive today may live to see this world - what will it be like?

There would be countless benefits from space to help the Earth - almost unlimited energy, no more dirty mining, minerals and rare elements in abundance. But also many challenges also. How can we make a safe transition to a world where every country and many private individuals have the ability to fly at speeds of satellites or faster - to anywhere in the world? Also interstellar travel of space probes at least might not be so very far away - at slow speeds, but perhaps with surprising implications for the future of humanity.

First though, let's look at some of the ways it might become easy to go into orbit.

RECOVERY OF INTACT BOOSTER STAGES

First, let's look at SpaceX because they are in the news, and are closest to actually achieving low cost flights to orbit, even interplanetary flight - though they probably have a fair way to go to reduce costs to match an airplane flight over an ocean.

Their innovative idea is to re-use the first stage boosters for the rocket. These are expensive and complex engines that are just thrown away and destroyed with most rocket flights. It's like building an airplane for a single flight, to do that and it's no wonder spaceflight is so expensive. Even with SpaceShuttle, the boosters were discarded after each flight.

Their spacecraft will have that capability also, to land like a helicopter.

The way SpaceX are going, perhaps in a few years rocket flights like this will be routine, hugely reducing the cost of going into space.

FLYING DIRECTLY TO ORBIT

This is a UK project, called Skylon, a jet that can fly directly to orbit. It would launch from an ordinary runway - like an airplane - the runway needs to be strengthened but is otherwise normal. And it doesn't need booster rockets at all, it carries all its fuel on board.

It burns a mixture of hydrogen and oxygen, but in the early stages it gets the oxygen from the atmosphere. It does that by a remarkable system that cools down the incoming air by 140C in a hundredth of a second, so can take in the air and still use lightweight materials.

has a massive reduction of fuel needs because it is air breathing in the early stages of its flight.

This is under active development right now, they are working slowly but steadily towards their goals. So one day it might happen.

SINGLE STATE TO ORBIT ROCKETS, LANDING AND TAKING OFF VERTICALLY

This is the classical "rocket" of science fiction and it's been explored many times.

This is a 1970s idea for a single stage to orbit vehicle, which would land like the SpaceX booster after delivering its payload to orbit. Nothing is discarded. This shows the return:

And this is the vehicle itself. It makes sense to return base first because that part of the spacecraft is already designed to withstand high temperatures.

There were earlier ideas also, in the 1960s, and earlier. Here is the 1960s Douglas SASSTO artist's impression.

One of the most developed ideas to date is the Delta Clipper. This was able to take off, and then land again, just like the SpaceX rocket, but this is back in 1995.

It was only intended as a proof of principle, and wasn't capable of gong into orbit at this stage. But eventually it could have become a fully automated, reusable, single stage to orbit space shuttle for unmanned cargos - and it could also take humans - who wouldn't need to pilot it as it was fully automated.

NASA took on this project but soon cancelled it, after a crash, and instead worked on the Venture Star, an innovative replacement for the Space Shuttle. But perhaps it was a case of too much too soon, that project also failed.

There have been many many other ideas for single stage vehicles to orbit and low cost ways to get into orbit or for sub-orbital flight. Many of these are no longer under active development.

AIRSHIPS TO ORBIT

A balloon filled with hydrogen or helium could rise almost indefinitely - if the skin is light enough, even close to the boundaries of low Earth orbit. This is a very low cost method because no fuel needs to be expended to do the lifting itself.

JP Aerospace plan to make airships that would rise to orbital platforms at 200,000 feet - so that's 60 km, in the mesosphere - above the stratosphere, near vacuum conditions.

They have the current altitude record for an airship for an unmanned but manoeuvrable airship of 95,085 feet, or 29 km

JP Aerospace plan to build airships that set off at a level higher than the highest flying balloon ever - huge airships made of such light materials that they couldn't be inflated at ground level.

These would be truly orbital airships - slowly accelerating to Mach 20 and greater.

When they set off from their base station at 200,000 feet (60 kms), they would be just floating. It's almost a vacuum inside the ship, yet still, because it is filled with hydrogen or helium, contained by the skin, then the lighter atoms of hydrogen or helium will float on the denser almost vacuum of oxygen / nitrogen outside it.

They would accelerate to orbit slowly over several days, by using ion thrusters. First they use a combination of lift and velocity - and eventually travel at orbital velocity at levels too high to get noticeable lift.

This idea of Mach 20+ airships accelerating to reach orbital velocity may seem absurd at first, it did to me when I first read it. But the more you think about it, the more it begins to make sense.

We launched several balloons to LEO in the Echo program, so there is no problem with balloons once they reach LEO. The problem is the transition between high altitude and LEO. For that, we want to find out about suborbital balloon flights. Those are rare.

An early experiment sent one of these balloons into a sub orbital hop which it survived for most of the hop and disintegrated eventually. When it did explode, this was mainly because they made a mistake and left too much gas in it.

That isn't much by way of experimental data, as this seems to be the only example of a suborbital balloon flight to date. Also that's with a small balloon not the huge kilometer scale airships of JP Aerospace.

Still, what data there is, is reasonably promising that the high speeds of the balloons won't be a problem so long as they are well above most of the atmosphere in close to LEO vacuum conditions by the time they approach orbital velocities. At any rate, JP Aerospace don't consider this to be their main challenge.

You can hear John Powell, the man himself talk about it in a recent Spaceshow talk, and decide for yourself. They have a very interesting philosophy also, it's a company that does its development in the slow lane. They've been working towards this for decades and finance their development by the discoveries they make along the way.

AIRSHIPS WITH FUTURE TECHNOLOGY

JP Aerospace are working within the limits of present day materials and technology. But what could the future bring for orbital airships?

We do have extraordinarily light materials we can create in small pieces and might eventually be make into large sheets.

Especially if you could make a balloon out of graphite sheets, for instance - and if you could make it impervious to helium so it can contain the gas - who knows how high a balloon could float with future materials just under its natural bouyancy? See for instance, Atom-thick carbon sheets set new strength record

Maybe airships made of strong materials such as this could fly all the way to orbit from the ground?

LAUNCH LOOP OR MAGLEV TRACK TO ORBIT

There are various ideas for ways to, basically, drive most of the way to orbital speed on a Maglev track.

A Maglev train is a natural for acceleration to super fast speeds of kilometers per second - as it has no on board fuel, gets all its energy from the track so no need to accelerate the fuel. And also as there is no physical contact with the track, friction can be almost zero.

First, there's the idea of some researchers for a long MagLev track which accelerates a spaceship inside an evacuated track up the side of a mountain, continuously until it reaches orbital velocities when it leaves the tube. They think this could cost $20 billion to build and it would cost about $50 per kilogram to get cargo into orbit, and the project would take about ten years to complete. For details see Maglev track could launch spacecraft into orbit.

That's for cargo.

You could send passengers too, but would need a longer railway line, and slower accelerations, would take longer to build and cost more.

Then more exotic, is the idea of a kind of "moving walkway" Maglev track, that elevates into the sky under centrifugal force". There are many ideas like this, but this is one of the simplest and most practical of them.

The loop continually moves around like a moving walk way from one end station to the other and back again. The loop is elevated away from the Earth by the centrifugal effect of the moving walkway. This centrifugal effect raises the centre portion of the track to about 80 km. Then, much as before, the vehicles accelerate along the track until they reach orbital velocity, and release themselves from the track to launch into orbit, See Launch Loop (wikipedia)

A surprising thing about these dynamic structures held up purely by kinetic energy of rapidly moving liquid or particles - there is so much energy in the system, and so little loss, that if you stop supplying energy, they lose it only gradually. It's rather like energy stored in a flywheel or a gyroscope. Stop supplying energy and the flywheel keeps spinning, it doesn't just stop instantly. They deserve close attention, and are not as way out and crazy as you might think when you first encounter them.

SPACE ELEVATOR

This is the idea of an elevator, just a cable that goes from the Earth's surface all the way up to geostationary orbit and beyond.

The physics is sound but materials are not yet strong enough to build it. Steel, titanium etc can support 20 to 30 of kilometers of its own weight in an untapered cable (can go up higher if the cable starts very wide and tapers).

For a tether able to go all the way from geostationary to the surface - well it doesn't need to support it's weight under full gravity all the way, but it still turns out, you need a material able to support thousands of kilometers of its own weight of cable.

For that you need carbon nanofibres, which are just strong enough - but with no safety margin, and in any case can only be used to make tiny, microscopic even, sections - certainly can't yet be made into a long cable.

The details are pretty well worked out, ready for some future time if we have a strong enough material. We might have this in a few decades. You'd need a counterweight to keep the cable stretched and the cable would go beyond geostationary orbit.

It would then be very easy to go into space. The gravity goes down slowly as you go up the cable, is zero at geostationary - and then you get the centrifugal effect pushing you away from the Earth after that. Spacecraft could accelerate along the track away from the Earth just under the centrifugal force and build up speed in that way - assisted if needs be by MagLev driving along the track.

However, you don't even need to do that with a space elevator. Just by releasing payloads at various points beyond geostationary, they have the delta v needed to go to various places - either the moon, or elsewhere in the solar system. Indeed if you just release a spaceship from the end of the tether and it has enough delta v to go to Jupiter without need to use any rocket fuel at all to do it Space elevator - launching into deep space

That's for the future of course, as we don't have the materials yet to build it.

LUNAR SPACE ELEVATOR

But you can do a space tether from the Moon with existing materials. because of the lower gravity.

The best way is to do it from the center of the near side of the Moon going up through the L1 position towards the Earth. You could build that out of kevlar for instance, though the authors take as their reference material a similar stronger material called M5 fiber

It is something you could, at least according to the author of the paper, do within the budget of a return of humans to the Moon, and could launch tens of thousands of tons of material from the lunar surface which you could then use e.g. to build settlements in space or whatever, Might be a better way of doing that than the rail guns of the Stanford Torus design.

SPACE ELEVATORS FOR ASTEROID MINING AND ASTEROID DEFLECTION

You can also use elevators for launching materials from rapidly spinning asteroid. Asteroids normally do spin, and if your asteroid rotates quickly enough, you can attach a space tether to it. Then you can use that to launch materials to the Earth, or anywhere else in the solar system you need it.

DIVERTING ASTEROIDS

You can also use a similar system for diverting asteroids. If it's projected to hit the Earth, and spinning, as most do, you could attach a tether to it, and by mining the asteroid and sending the material away from it in calculated trajectories (hopefully do something useful with the material at the same time) you could divert its course.

Another idea involves a permanently attached counter weight to change its centre of gravity and so its orbit. It is a minor effect in this case, but someone looked into it and found it could make a difference for light weight comets and asteroids. See news article - and then the paper: Asteroid Diversion Using Long Tether and Ballast

USING A TETHER FOR A SLINGSHOT CHANGE OF TRAJECTORY AS YOU PASS AN ASTEROID

This is perhaps a bit of a digression from the main theme, but while we are on the topic can't resist mentioning it as it is such a fun idea.

Tethers can also be used as a way for spacecraft to do a slingshot type change of course - but instead of using gravity as you do for huge planets - instead it just throws out a grappling hook, as it were, on the end of a long tether as it approaches. This then diverts its course around the asteroid, and then when it reaches its desired course change, it releases the tether.

ROTOVATOR TO SNATCH VEHICLES OUT OF THE ATMOSPHERE AT MACH 12 AND PUT THEM INTO LEO AT MACH 25

You also have the idea of a Rotovator, - this is a tether that's not permanently connected to the ground, but instead - e.g. for the Moon - you have it spinning around a center of gravity in orbit - and once every orbit it touches ground - and you arrange it so that it is spinning against the orbital velocity in such a way as to exactly balance out, so that it's stationary relative to the ground when it touches the ground. So then you can put materials into it at that point and is an easy way to transfer those materials into orbit.

This animation of a rotating wheel with a point on the circumference traced, shows how the rotovator is able to achieve zero horizontal velocity as it approaches the ground. It's similar to the principle of a wheel in transport - though a car moves at great speed, the portion of the wheel that touches the ground, momentarily, doesn't move at all.

You can have similar ones like that in Earth orbit, but of course not touching the ground, and you can have shorter ones - so the lower tip is simply rotating at a rather slower orbital delta v so easier to get to from the ground, gets rid of the need to accelerate once you get into orbit, or not so much.

And one idea takes that a bit further, and has the tip actually extend down into the atmosphere. Although with existing materials it couldn't be stationary at the Earth surface, it would be able to snatch a rocket or extremely fast aircraft in a suborbital trajectory --, and fling it into high orbits.

This requires constant input of energy as the tether would slowly de-orbit - loses delta v every time it does one of these gravitational assists. But it can get the energy back again by using solar power and then sending electric current along the tether to accelerate it back into orbit using the Earth's magnetic field for a motor.

T hen finally, remarkably, you can have a complete transportation system combining a rotovator in lunar orbit, and a gravity assist tether bolo in LEO - and then because the Moon is higher in the gravity well, if you arrange things carefully, then simply by dumping lots of lunar dirt into the tether system continually at the lunar end - that can power up the whole system, giving all the energy you need to send materials from Earth to the Moon - and simultaneously transferring lunar materials to LEO or to the Earth itself. See the cislunar tether transport system architecture

WHAT IF WE CAN FLY INTO SPACE AS EASILY AS WE CAN SAIL OR FLY OVER AN OCEAN?

We have a billion airplane flights a year at present. What would the world be like if we had a billion similarly priced flights into space every year?

Then, what if we can get into space as easily as we can sail a boat across the ocean right now?

If any of these ideas come to fruition, that might be the reality, say 50 or even 25 years from now. After all 25 years ago (the 1990s) hardly anyone had a mobile phone, the internet was in its infancy, didn't have GPS, or skype or facebook etc, we were still in the cold war and hardly anyone had heard of global warming.

BENEFITS

There would be many benefits for sure. Easy to construct solar power satellites to beam clean uninterruptable energy back to Earth. That could mean an end to global warming issues, and low cost electricity for everyone. That would benefit the poor people most of all.

Then, in same world, we'd have low cost materials mined in space, moving all the "dirty" mining technology away from Earth into space where, if we are careful, it can do no harm, in the vastness of space.

And fast transport on the Earth - could go from Europe to the US with only 12 minutes travel time (though surely with overhead in the airports, and launch and take off).

There would be countless benefits like that.

BEAMING SOLAR POWER FROM SPACE

This might be the first and most immediate benefit from space industry for the Earth.

Either the satellites are light weight and sent from Earth - or costs to launch from Earth have gone right down - or they are constructed in space. There have been many ideas like this, back to the Stanford Torus design and earlier.

The big advantage over Earth based solar power is that solar power in space is uninterrupted, while solar power on the Earth is interrupted by night, and clouds, and by the long winter nights in the higher lattitudes.

We do get plenty of solar power on the Earth - and now we also have methods of long range transmission. It might be, that solar power and other renewables gets cheap enough, and storage capacity increases enough, so that we don't need to think in terms of solar power satellites to solve our energy problems.

But solar power from space could be a significant part of the mix for a clean energy source in the future.

There are various ways to make it safe to beam energy from space. One of these is to use many low energy beams, designed in such a way that they can only focus on a ground station if it gives them a beacon to aim at - and make sure that even when focused like that, energies are so low it is eye safe. With these designs, you could walk right through the collection area and look up at the solar satellites and still not damage your eyes. See for instance Space Based Solar Power (SBSP), at Airbus.

MINING IN SPACE

Mining in space might be easier than you would think. Yes, of course, it's pretty hard to get the mining gear to the asteroids in the first place. But once you've done that- and you only have to do that once, or rarely - getting space materials from space back to Earth could be easier than you'd expect.

First - since you only have freight to transport, it's like shipping oil or ore, there is no hurry. You can use solar sails and gravity assist and trajectories that involve multiple flybys of the Earth, Moon, Venus or Mars also if it helps, depending on the original orbit. It might take years to return your cargo, but if it costs much less per ton to do it that way, you would probably do it.

There are many NEOs that come close enough to Earth to make return of materials relatively easy and they would make attractive first targets. You can also use the mini space tether idea to use natural rotation of the asteroid to propel the materials into space - in that case then they might use hardly any fuel at all to get back to the vicinity of the Earth.

That gets it back to the Earth Moon syste. To return materials to Earth, you have to target the Earth's atmosphere and to hit it slowly enough so that the materials you mine don't burn up in the atmosphere. You might do aerobraking first to reduce speed, and then over a period of time, skimming the atmosphere, lower the orbit to make the landing gentler.

When you are ready, then actually landing the materials on Earth is relatively easy. To make sure there is no risk of damage to Earth, if the parachute or aeroshell fails to deploy, make sure you send the materials in small amounts, small enough to burn up in the atmosphere in its entirety without the aeroshell - and equip each one with an aeroshell and parachute.

Conventional aeroshells are likely to be too complex to create on-site at least at the early stages of development, and too heavy and so too costly to export from Earth. But there's an alternative here, the ballute, an inflatable balloon that works like an aeroshell

Space mining would probably start with mining of water from asteroids, for use in LEO and other spacecraft missions, as suggested for instance in this article Asteroid Usage by Planetary Resources, an asteroid mining company - because of the high cost of supply of materials to orbit, making it far easier for the mining to turn a profit and pay for itself. But later, funded by the sale of water to space agencies, it could then move on to mining metals and other resources useful for Earth itself.

DIRTY INDUSTRY IN SPACE, AND WASTE DISPOSAL

This is a natural thought as a way to dispose of high level nuclear waste, if you can get safely to orbit. With low cost transfer of materials to space, if you could do it safely as well, you could send any extremely hazardous waste into space.

You could fire it into the sun. The numbers though don't add up, it's really hard to hit the sun from the Earth as you have to counter nearly all of the Earth's orbital velocity one way or another - by rocket launch or by flybys.

You could, more cheaply, send it into interstellar system, out of the solar system. once you have ways to send material with escape velocity more easily. See Shooting for The Sun

Still, sending hazardous wastes into space and into the vastness of interstellar space has its attractions once spaceflight is far lower cost especially if you can send non living cargoes into space for dollars per ton. Perhaps have reprocessing facilities in space.

It's the close proximity of Earth life that makes the wastes hazardous on Earth. In space, with no living creatures to be harmed by them, then it's not the same issue. You need to make sure they won't get back to Earth or anywhere else that will be hazardous for life.

Perhaps they even be useful in space for various things.

One might well have mixed feelings about mining the asteroids or sending wastes into space or doing industrial operations with hazardous biproducts in space.

Space is vast and the asteroids numerous almost beyond imagining. Yet - some feel unsure if we should exploit it at all.

Still, we might well do, and the benefits for the Earth could be huge. If you have thoughts about this, do say in the comments!

FAST TRAVEL

Our rockets or planes might not only thrust during lift off. They may have powered flight throughout the entire orbit by then if we have, e.g. easy portable fusion power.

If you can do that, then you are not limited to the 90 minute plus orbits of normal satellites.

If you travel fast enough to have a 1 g force outwards away from the Earth, comfortable for humans used to full g, then you can go round the entire Earth in 60 minutes. Increase that to 3.45 g outwards artificial gravity, which many will be able to tolerate for a while, and you can get around to the far side of the Earth in 20 minutes.

By then, the ordinary everyday "planes" may also be able to travel as far as other planets and the outer solar system, with journey times of weeks or days - if you can do continuous thrusting at one g, you can get to various places in the solar system very quickly.

HAZARDS

So, there could be many benefits. But, there would be issues as well. What kind of a world would it be where just about every single country and many large companies have the capabilities to launch intercontinental ballistic missiles?

Your ordinary "plane" 25-50 years into the future is likely to be as fast as present day ICBMs, or most likely faster if they have this capability to accelerate throughout the flight.

How can such a world be a safe place to live in? Well I think it's pretty clear it wouldn't be if you were to suddenly give that technology to all the countries on the Earth right away. But we have technology now that would be just as hazardous to world peace if we magically sent it back 50 years to the 1960s.

TRANSITION

Can we make the transition to such powerful transport methods safely? If so how?

And what happens about property rights in space. Would we end up having nations trying to carve up territories in space? Could we have wars in space? Those would probably be fatal for all concerned in such fragile communities. Any space station or space colony, say on the Moon, has to contain ten tons of air pressure per square meter, and the spacecraft themselves are traveling at immense speeds, any station would be hugely vulnerable to an adversary who wants to destroy it.

If we ever did have an all out war in space, using fast spacecraft with advanced technology, probably there would be almost nothing left a short while after the war started.

And what would happen in the inevitable conflicts of interest between the various groups of people in space?

These could include:

Scientists who want to study the solar system in its pristine state

Exobiologists who want to keep many places like Mars, Europa, possibly even areas of the Moon, uncontaminated with Earth life

Engineers who want to use the materials to build things

Miners who want to extract materials from space to sell, or use on Earth or to make solar satellites etc

People who just want to go everywhere as tourists and potentially contaminate sites of special scientific interest with Earth life

People who just take things of scientific value away as souvenirs

And many others with various agendas for space, bound to conflict from time to time

REASONS FOR OPTIMISM

Well there is some reason for optimism. We have already got technology that, back in the early C20 would seem just as bewildering and impossible to imagine how we could handle it safely. But somehow we have, with some major hiccups but with many internationally accepted rules and guidelines that make present day society work,

So, I think we'll manage it, hopefully. And it's probably no more possible to have an accurate idea of how it will happen as it would be for someone 50 years ago to imagine how the world would work today.

But it can't do any harm to think over the consequences in advance. I think we have an excellent start on this with the Outer Space Treaty which helps to protect nations and promote peaceful uses of space. Also I think it helps that there is nowhere in space that is, in its natural state, anything like as habitable as the Earth. And the OST already protects habitats that you make yourself. So we could build on that to have laws in space that work, without need to designate territories in the solar system to assign to particular nations or entities. Rather we could use a functional type of ownership in space.

Legal Property Rights under the Outer Space Treaty

"... Ownership of objects launched into outer space, including objects landed or constructed on a celestial body, and of their component parts, is not affected by their presence in outer space or on a celestial body or by their return to the Earth..." . (Outer Space Treaty)

This has been interpreted as meaning that if you construct a habitat on the Moon or use materials from an asteroid to construct a habitat in space, that you own the habitat though not the Moon or asteroid.

If understood this way, it could be a basis for laws of functional ownership within the context of the Outer Space Treaty. See the article at spacefuture.com by Wayne White: Real property rights in outer space. This is a matter of a fair bit of discussion but it does seem at least possible that one could develop reasonable laws of ownership within the context of the Outer Space Treaty.

Assuming that we do make it into space, peacefully, without destroying our civilization, then there are many other questions and issues to think about.

It's about an idea to send a stream of mini solar sails - each one is just a pellet in a Mylar sheath - as a way of refueling an interstellar spaceship in flight, throughout its early acceleration phase from Earth. The solar sails are accelerated close to Earth, so you don't have the spreading problems you get if you try to transfer laser power all the way to a distant interstellar spacecraft. This lets you transfer energy from Earth all the way to the interstellar spaceship at high efficiency throughout the long acceleration phase.

You could just use the momentum of the solar sails for acceleration, as in this earlier concept by Jordin Kare Sailbeam (slides) - Paper (to get an idea of how it works see the Figure 1: SailBeam Concept in the paper). Jordin Kare thinks there's a chance you could manage 0.1c or faster with this method.

Then the deceleration phase can be simpler. The spacecraft generates a magnetic field which acts as a brake against the solar wind of the destination star. In this idea, it uses a superconducting coil to generate the magnetic field

A similar idea to the MagSail is the Electric sail (or e-Sail) which is being investigated by the ESA as a way to propel spacecraft to the outer solar system, it uses many thin wires spreading out from the craft, and an electron gun in the centre fires electrons away (shown blue below) thus creating a current which flows in from the wires to the centre - this creates a magnetic field which makes an obstacle to the solar wind - rest is as for the MagSail, here is an artist's impression.

The paradoxical thing about interstellar travel is that so long as the timescale is of order of centuries, it's worth your while waiting for the technology to improve as otherwise later departures get there before you - until the time required goes down to a few decades. But if timescale was just 44 years, could be worth setting off right away.

Surely we will send unmanned probes first before we attempt humans with all their life support?

An even faster way to get there is being explored at the University of Michigan, the Nanofet drive, which fires minute particles at close to the speed of light, originally designed for tiny spacecraft

There would be many practical issues with a big spacecraft going close to light speed through the interstellar medium, but this at least gives a possible future method you could achieve those velocities.

Another more way out idea being researched, Quantum vacuum plasma thruster - idea is - to separate out particles from quantum fluctuations on the vacuum and accelerate this as your reaction mass so you don't have to carry it with you..

and lots of other ideas.

COLONIZING GALAXY - SHOULD WE WORRY ABOUT FUTURE INVASIONS OF EARTH BY - OURSELVES?

Personally I'm not at all sure we should colonize the galaxy, though great to explore it. The problem is, that if, as the author of that paper suggests, humans fill the galaxy quickly, say in a million years or so, then - what would all those humans turn into?

We worry about aliens invading Earth. But it's pretty clear that no alien species have colonized our galaxy yet, and it would be just an extraordinary coincidence for one to arise today, within a million years or so of humans, out of the billions of years since the galaxy was born. If they were at all like humans as we are now, and colonized the galaxy, then some of them at least would probably have colonized Earth itself long before we evolved, and transformed it to their liking (maybe changed atmosphere and planted their own biology).

Actually, an ET probably wouldn't bother to take over the Earth, they'd have the technology to easily reproduce anything they want - and you can use the materials from comets and asteroids to make habitats in space which would give far more living area than the surface of a planet.

With the technology an ET would have after a few million years of development they could do that easily at almost no time cost to themselves, just set some automated robots working for a few years and you have your Stanford Torus or whatever in space to live in, and probably only a few years after that, exponential growth, have living area as large as they want of these habitats scattered through the solar system, made of materials from the asteroids and comets, hundreds or (if they used materials from the Oort cloud for instance) thousands of times the surface area of the Earth.

So, if they were like us, and really were also keen to colonize the galaxy, then by now the entire solar system should be full of their free floating habitats in space. You just need to look up at the night sky - that we don't see the sky filled with bright lights of ET spacecraft and space colonies shows that no ET has set out to colonize the galaxy - or at least not successfully.

If there are ETs then for whatever reason, they clearly aren't the galaxy colonizing or planet occupying type.

Humans, though, if we spread at our present stage of civilization, some of use at least are like that, and they would be the ones who would end up doing the colonization, if they survived.

JUST BECAUSE THEY ARE OUR DESCENDANTS, OR CREATED BY OUR DESCENDANTS AS MACHINES OR BIOLOGICAL ENTITIES - DOES NOT MAKE THEM SAFE FOR US

So, I think we should instead worry about future humans and things they create - as potential Earth invaders rather than ETs. Just because they are our descendants a thousand generations removed, doesn't mean that they are going to be kindly disposed towards Earth and leave it alone, and be more gently disposed to us than ETs.

Plus, they could also trash the galaxy by accident. We almost have the technology to do that already - if you can make a self replicating self improving "Von neumann" machine, basically just a nanoscale 3D printer able to print out a computer chip and to make copies of itself - and it could spread just as life does, but using asteroids and comet materials to make copies of itself.

Rep Rap printer making a copy of itself (the "Child" in the photograph).

The RepRap can only make about 50% of its components so far, but the Rep Rap project is working on ways to increase this - eventually once they can print out electronics, 3D printers may be able to make a complete copies of themselves, and then rudimentary Von Neumann machines may not be far away.

A future Von Neumann machine could be programmed to make paperclips as well as copies of itself and to improve itself in evolutionary fashion to get ever better at making paperclips.

If set loose on our galaxy without proper controls, it might turn the entire galaxy - asteroids, planets, dust clouds - eventually stars, turn everything into paperclips - all the time getting better and better at doing that as time goes on - and from something simple and crude created by a paperclip factory owner with interests of profit, evolve, like life, into things powerful and almost impossible to stop.

Von neumann machines are great assets of course under proper control, could enable us to do mega-engineering projects of great benefit to humanity at almost zero cost. E.g. self replicating solar panels in space, or on the ground, making solar panels for instance, from desert sand and using sunlight as the energy source (some future version of the Sahara Solar Breeder project perhaps).

But they do need care also. Perhaps a galaxy full of human colonists couldn't be totally relied on to take that level of care with them, someone amongst those countless trillions slips up and you end up with a paperclip event horizon or worse.

This may seem like science fiction to you. But many things that are part of our daily lives now were similarly science fiction fifty years ago or even twenty five years ago. Von Neumann machines do seem to be things that are engineering possibilities in the not too distant future, and once you have them, even on a macro scale, not the more exotic microbe like nanoscale von Neumann machines, then it opens out possibilities like these.

DO YOU HAVE A SOLUTION TO THIS?

I don't know why people simultaneously want to colonize the galaxy - and then - worry about ETs invading Earth. It seems an inconsistent point of view to me.

The only ETs likely to be a nuisance to us are ones that want to colonize the entire galaxy. So we worry about them, and hope they don't exist. But at the same time, want to turn into such an ET ourself.

Although of course it isn't presented like this - seems to me that if you look at this without Earth chauvinist spectacles, that it would seem, for instance to any ET who listens into our discussions, as if we keenly desire to become the very type of alien monsters for the rest of our galaxy, that we worry might, as ETs, cause a nuisance for our own world.

If that's it, maybe it's just because we are a young species. Perhaps all ETs go through this stage in their youth as a technological species?

Or, maybe I've just missed something obvious. If so what is it?

I've posted about this a few times in various places, mainly comments on my column at Science20. It's generated a fair bit of discussion but to date, I've not had any truly reassuring answers to explain how we can colonize the galaxy in a safe way and be sure this won't happen.

Do you have an answer to it? I'd love to hear it if you do. Say so in the comments below. Any ideas for how colonizing the galaxy by humans can be done safely, without a significant risk of trashing it both for ourselves and any future evolving ETs around other planets in our galaxy?

EXPLORING - IF THERE ARE ETS MAYBE THAT'S WHAT THEY DO?

Of course if you stick to just exploring, not settling down anywhere except a few firmly delineated safe places, with some way to be pretty certain that humans won't spread beyond them permanently - but can explore as much as they like - it's not a problem.

Also nomadic colonies traveling through the galaxy are fine, so long as there is something that limits them, prevents them from splitting up into more colonies as time goes on - or do so only very very slowly like very few billion years.

Perhaps this is what ETs do, if they exist. Perhaps reckless ETs destroy their civilizations at an early stage, and if not destroyed already, destroy themselves as soon as they colonize space, through space wars.

While more cautious ETs, maybe they are also naturally far seeing, and ask themselves, what will the consequences be of colonizing the galaxy a few centuries, millennia or millions of years down the road?

They may also have learnt to extend their lives by then so they have lifetimes of thousands or millions of years - making these consequences not just for their descendants, but things they might encounter themselves later in their lives.

That's likely to give you a different perspective on colonization and exploration of the galaxy. They may not need FTL (Faster than Light) travel. You'd be able to do a galaxy tour in your own lifetime at liesurely sublight speeds, if you so wished.

Conversations between ETs could also be leisurely things that last for millennia. Maybe we are due a visit by an ET, but next time they come this way will be a few thousand or million years from now, a short time for them. Maybe they will say "Hi" to us some time in the next thousand years or million years.

I think that's actually pretty likely, that an ET with millions or billions of years of civilization, would have learnt to extend their life-spans, and so have a much more leisurely pace of life than us.

Though, perhaps equally likely that we are the first ET to evolve in our galaxy with spaceflight and astronomy.

There might be non technological ETs or ETs that are living in subsurface oceans of icy moons like Europa that don't know the rest of the galaxy exists. Again I feel that's quite likely, depending on how likely it is for life to evolve in such places. There are probably many more habitable subsurface oceans in the galaxy than habitable planets. If so then we may be unusual as a surface dwelling species.

CONNECTION WITH FERMI'S PARADOX

There's a connection here with the famous Fermi's paradox of course, the paradox that the galaxy seems old enough for many ET civilizations to have arisen, yet it would just take one of them to colonize the galaxy, within a few million years at most. So why aren't they here?

I don't want to go into that here, the main focus here is, can humans colonize the galaxy safely, or is that impossible, should we make sure we don't colonize and only explore?

It's a possible explanation for why the ETs aren't here. But they might not be here for many other reasons including the possibility that we are the first technological ET in our galaxy with the capability of space flight. We would still be faced with this question, can we safely colonize the galaxy - safely for ourself - and safely for any other potentially vulnerable ETs there may be in the galaxy?

There might be highly intelligent, peaceful, civilized ETs for instance, maybe far beyond us in the realm of mind and thought and ideas - and lifetimes of thousands or millions of years, maybe their medicine also is far beyond us - perhaps largely based on holistic methods - with almost nothing we recognize as technology. Maybe they live as dolphins or whales or octopuses in oceans. Maybe they are terrestrial but small and weak like intelligent parrots, without the dexterity or strength to build spacecraft. There might be many possibilities for intelligence, awareness, feeling, kindness, abilities far beyond ours.

Yet they might still be vulnerable even, say, to a single Earth microbe invading their planet, loaded with what, to them, is XNA. For them, we, or our microbes even, would be the terrifying, alien ET monsters.

COULD WE FIND A WAY THROUGH THIS?

I am cautiously optmistic that somehow we'll find a way through all this. Maybe we will make contact with ETs in our galaxy, or detect signals from ETs in another galaxy who have already encountered these issues.

Maybe we'll even spot a distant galaxy that's been overrun by Von Neumann machines or been totally colonized by ETs and so have an idea of what is likely to happen to our galaxy if that happens.

But it might be that we are the first or almost the first in our galaxy, even in the universe, to face these problems. Or it may be that other ETs are just too far away and communicate too rarely to be of much use to us as a way of learning what can go wrong.

If so we'll need to find a way through by ourselves, and it will, I think, be a matter of much discussion over the next few decades and centuries, if we continue as a technological species.

Maybe we'll find a way to colonize safely. Or maybe, we'll decide we have to explore the galaxy only, and evolve a "prime directive" of non interference much like Star Trek.

I don't expect any final answers, but what thoughts do you have on all this?

Comments

Excellent article! I'm looking forward to reading all of it.
Adding to your list of affordable ways to leave Earth, I want to remind of "Microlaunchers", the simple idea to make probes so small that they can launch with small conventional rockets. The idea driver Charles Pooley has test launched a sounding rocket made out of an irrigation pipe and he has a probe design based on cheap off-the-shelf components (and a more expensive upscale amateur telescope to receive data from the probe's laser beam). The vision is to grow a new garage rocket industry from the bottom up, much like home computing has grown.

Interview(graphic shows the interplanetary super highway - once you have microlaunchers to escape velocity from Earth then in principle the cubesats could go anywhere in the solar system - or even with less velocity using solar sails and lunar flyby).

BTW I forgot to say anything about the idea of firing rockets and propellant to orbit using a gun, mentioned it in the intro but then forgot about it.The slingatron has a spiral track, and this spins at 60 rotations per second with off centre axis, if I understand right, so oscillates like a hula hoop, put a projectile in the centre at the right phase in the oscillation and it gets continuously accelerated, and if the circular track is long enough, can reach orbital velocities quickly within seconds, under hyper gravity.

"The Slingatron is a brilliant idea based on old-fashioned mechanical engineering . It could be used as a public-highway space-transport system, reducing the cost of launching freight from the ground into space by a factor of a hundred. This book explains in detail how it works, and how it might be used for many mundane purposes besides space-launch." --Professor Freeman Dyson

I think this is am interesting idea, if they can prove it works, for things like rocket fuel, water and such like supply to orbit. It could also be used, the authors suggest, for fast low cost supply of materials to disaster areas, sending smart ballistic containers in a stream as food aid, water etc to anywhere in the world where it is needed, and various other applications.

Downside is, high g forces, so probably not a good idea for micro-satellites and no use for humans - but great for water, fuel and other such supplies, very low cost - just like firing bullets to orbit basically most of the launch system remains on the ground - need a tiny, robust, second stage, the projectile itself goes into space with velocities of 6 or 7 km/second depending on the size of the Slingatron, then second stage circularizes it and adds a bit more boost.

2) Starting with maximum velocity.
It would be like a small asteroid hitting Earth, but starting with the impact. BOOM! What would remain of their shaking gigantic spaceport after this nuclear weapon sized launch effect has happened in its muzzle?

I'm a regular follower of nasa advanced concepts forum, your article is a nice overview of ongoing ideas for more affordable space access.

One rarely discussed aspect is environmental impact of a massive space industry, space launches on the same order as air flights say. Given the energies involved, if they are not much more cleaner and "green" than usual approaches, that might hurt atmosphere. Even apparently clean H2/O2 chemical propulsion releases high temp. gases (producing NOx) and water at altitudes where it might have some effect if massive amounts are released ( water vapor from shuttle launches could be followed to the arctic : http://www.nasa.gov/mission_pages/aim/news/shuttle-exhaust.html#.U3OWoij... )

That + H2 production is far from carbon neutral (with today economic process) could make a massive use of chemical rockets a real ecological problem, (or boon if it would by chance counteract global warming ?) Any studies on that ?
Even mass drivers (driven by supposedly clean electricity) would release significant NOx levels given the extreme speeds in air, although it should be compared to naturally occurring hypersonic entries of meteorites, few 10000's of tons a year, much less when considering bigger bodies. But if mass drivers (slingshots...) send mass to orbit for less than 5$ a kg we might consider sending million tons...

What would be the cleaner concepts in the list given ?
Space elevator would seem the cleaner but requires yet to be proven specific strength bulk material.
JP aerospace airships ? I'm still struggling to understand how they could go from a buoyancy lift to orbital speeds without a hypersonic lift phase, how could drag be much less than aerodynamic lift for that to be efficient ?
My feeling is that so far the cleaner concept for massive launches is launch loops (space fountains...) where the acceleration to orbital velocities is done outside (or mostly so) outside the atmosphere, and without expelling any reaction mass.

Yes interesting thoughts. I'd have said the airships sounds the cleanest also, of the ones we can do right away. Speaking as someone with a long term interest in scientist, but mathematician by training and no engineer or expert in this...

Not sure about the issues of NO2, it's a good point, that something that's a non issue if you are sending a few tons into orbit could become a big issue if it starts to be millions of tons. And releasing huge amounts of water vapour at altitude - yes can imagine that having climate effects.

With the airships, there is a bit of an issue there that helium is something of a scarce resource on the Earth if you want huge quantities for airships. However - eventually - they could use hydrogen quite safely up at the higher levels, indeed there's a sport of hydrogen ballooning, what they call "gas ballooning" which in Europe uses hydrogen, it's not nearly as hazardous as the Hindenberg disaster suggests, so they say. Though they are careful to avoid thunderstorms (a conducting balloon cover would help there but still...). If anything did go wrong, you've got a long way to fall, plenty of time to deploy parachutes or whatever is your fallback safety measure for the passenger or cargo compartment.

But - you'd be going well over Mach 20 (7 km/s) to completely counteract gravity, and surely, you can't go that fast in a balloon until you have almost no drag.

So yes, I don't understand either - okay at 200,000 feet just lift. Could still be lift all the way up to 300,000 feet or more, if we suppose that the balloon is light enough so it can be 1/100th of the weight of a conventional airship (say) - just picking numbers out. But then it has to be much larger, so when eventually you start to accelerate, similar amount of drag, you'd think.

After that, could it be that they aren't just using hydrogen as a lifting gas, but also, the wings as a lifting surface? So, surfing over the near vacuum of the air, when they are too high up to get significant lift, but low enough to get significant drag?

I think they must be. But not sure it really explains how they deal with the stage in the middle, where they approach the speed of sound, then going supersonic, with not nearly enough speed to be in orbit or gain significantly from pure speed. I think has to have some element of conventional lift like an airplane?

They seem very confident, and have been working on it for a long time, but haven't seen any detailed calculations of how they plan to do it.

Also- the maglev - guns to orbit, or whatever - if they have secondary stage boosters to circularize the orbits - what effect would all the fuel exhausts of possibly many billions of secondary stage boosters every year do to the upper atmosphere?

I think they are good points, don't know enough to say how much of an issue it is or what the answers are and don't recall any papers on this, good thing to try to find out more about! Anyone else reading this know more about this or got any thoughts about it?

Concering contact with ETI, I think that the speed of light limit, makes every kind of large scale interstellar social coordination impossible. There's no way to stop further out colonies from developing very differently.

Coordination will break down when it takes thousands of years to get an answer. Even those who signaled the order will have changed so that they won't be interested in it anymore when the reply arrives. Every colony mission could have continuous communication with its "mother ship", but as the lag increases with distance, interaction will degrade and become irrelevant. They would only be sending each other their history books.

And pre-programmed von Neumann machines, like the paperclip factory, will be inferior to those who adapt dynamically and who use their energy to produce their own survivability rather than useless paperclips. So adaption is necessary, and conditions will vary. Every ETI will have its own unique path and differ much from most other ETI's, I figure.

We shouldn't bother about their intentions, if they haven't evolved away from such a phenomena, because there's nothing we could do about it anyway. They are probably here right now, but they ignore us and we cannot fathom how to perceive them. What do ants know of human civilization, even when they run across our kitchen floor?

Yes that is it exactly, same thing that I was saying also, about ETIs, I think we don't need to worry about them too much, because the chances are, if there was anything to worry about they'd have done it long before we evolved.

WHY WE PROBABLY DON'T NEED TO WORRY ABOUT ETIS

Chances are they aren't here because you'd expect to see some evidence of a galaxy wide ETI culture with every star colonized.

If they are here, and had any intentions of taking over the Earth they'd have done so millions of years ago before humans evolved - and instead - they have left our entire solar system in pristine state as far as we can see.

So can't be exploitative or colonizing by nature.

Could be they inhabit some different niche from us, e.g. live in the Oort clouds and the coldest regions of the outer solar system, and can't bear the heat of the sun as in one of the ETIs in Larry Niven's novels.

Or are hiding from us (zoo hypothesis)

Many other possibilities.

Or just not here at all (which I think myself is most likely).

WHY THERE MIGHT BE A SMALL CHANCE WE DO NEED TO WORRY

I'm not sure I'd go so afar as to say we totally don't need to be concerned at all. I think Stephen Hawking does have a point worth thinking about. With some of the solutions to the Fermi's paradox, then we do still need to be careful about contacting ETs, so it depends on the reason for the silence.

E.g. if you get periodic waves of civilization that then destroy themselves, or on going galactic wars, that keep numbers of ETs down with most of the galaxy barren - or if the galaxy is filled with Von Neumann machines already but many competing machines that keep numbers down by destroying each other.

So there are some scenarios, where we might not want to draw attention to ourselves.

Just think those don't seem that likely to me. I think that it's unlikely that an ETI could be pervasive in the galaxy, and yet such low numbers that we don't notice anything. I think would be an all or nothing thing, either ETIs almost everywhere, so are here already - or they are stay at homes or hardly anywhere and no interest in colonizing, not easy to get anything in between the two. But wouldn't go so far as to say the other possibilities are totally impossible.

ANALOGY OF ANTS

As for the analogy of ants - ants don't have telescopes, and can't reason from consequences, or build theories. If they could, then the scientists amongst them could deduce that we exist and learn things about us. I think ETIs could hide from us, yes, deliberately, or might be they have technology that looks like natural things to us, for some reason, or they could live on time scales that are far slower than ours, so look like unmoving rocks to us, etc, lots of possibilities.

But - don't think they will be invisible to us just purely as a result of advanced technology - has to be some more to it than that. We might not understand them, but we'd notice them if they were just advanced technology and doing megatechnology able to reshape planets and stars.

Also - not sure myself that they would be necessarily more intelligent than us. High technology could lead the other way - to lower intelligence because the machines do everything for you. It's not that clear that high intelligence is going to be an advantage to an ETI.

And however clever or intelligent they are, would have the same problems that humans face. They'd have wishes and desired, and frustrations of those wishes, happiness and sadness, and hopes and failures, just like us, I'm pretty sure. Some may have amazingly long and happy lives, but still. I think they would have things they could share with us and be able to learn from us just as we learn from them.

WILL WE BE THE ETI MONSTERS

But, whatever the answer there, the basic question still arises, however unlikely it is that ETIs will be problematical for us.

It's a question about us. Will we become those monsters ourselves?

LACK OF COMMUNICATION BETWEEN COLONIES

And indeed, the main reason I'm concerned about it is, just as you say, because of the break down of communication. No matter how civilized we might become in the future, maybe it would be just so unthinkable to create an unrestricted Von Neumann machine that we can be totally sure nobody in our civilization will do it - or have some fail safe way of detecting them and stopping them from spreading. But - that's all very well but what about those colonies who gradually spread beyond our range of influence, develop different cultures, regress, maybe become child like and forget the reasons for not creating von Neumann machines, just make them like children out of a sense of play and fun with no thought to the consequences. Or ourselves also if our civilization regresses. Or people motivated by short term goals, and don't care about what happens a century later to the galaxy.

It's that sort of thing I think needs answers.

PAPERCLIP MAKING VON NEUMAN MACHINES

Yes they could lose the ability to make paperclips. Depends on their origins I think.

If they just evolve like life, in an unrestricted way you'd expect them to soon lose their ability to make the useless paperclips.

But - if they are machines, they could be designed to evolve, but only within fixed parameters, so that they have to make paperclips, or they die.

Probably wouldn't be that hard to do. Some kind of feedback built into their design at a fundamental way strongly encoded and encrypted so that they can't do anything about it, or probability of a bypass mechanism evolving is tiny.

It just depends on the design, but - just as we could design safe Von Neumann machines to do mega-engineering tasks without causing any problems to ourselves, or the galaxy - so you could also design Von Neumann machines that are - almost safe - but some mistake in the safeguards - so that they only make paperclips.

I.e. are "safe" to that extent, that they can only make paperclips and copies of themselves - but they are also able to improve themselves and are not restricted in number.

Of course you could also have things that start off as paperclip machines and evolve away from that to do almost anything, as you say.

Or ones that are totally safe and only ever make paperclips and stop reproducing, say after 10 generations or whatever.

And in between, you have ones that remain as paperclip machines, but evolve to get better and better at it until they are almost unstoppable. But not to take this particular example of Nick Bostrom too seriously. Mainly I think it's a good one to use because it points us at this interesting borderline region between the carefully engineered safe VNMs and the totally unsafe unrestricted evolution VNMs.

It's just a rather fun whimsical idea, not an attempt at foretelling the future :).

:). Yes, suggests, an unsold spaceships event horizon, galaxy filled with spaceships created by Von Neumann machines - really useful things in moderation - but not if you find the machines are taking your home world apart to make them :).

The production and unuse of millions of new cars does take apart my houshold car and tax economy. (Similar policy has already taken apart my home economy). Economics of today jealously tries to challenge the numbers which astronomers use. Trillions and eternal debt and absolute zero interest rate.

On the other end you could expect some higher scale transition : interesting things happening when many simple things connect, the basic stupid process that's ruling the lower scale level being unaware it's being used by life "on top" of it.unlimited shapes with limited "atoms"
Also on cosmological scales, paperclips connected strings could create (implement) a Universe compatible with some string theories %)

quote op >>
And however clever or intelligent they are, would have the same problems that humans face. They'd have wishes and desired, and frustrations of those wishes, happiness and sadness, and hopes and failures, just like us, I'm pretty sure.
<<

Its always highly speculative to think about that (with ant minds) but, as it was already pointed out elsewhere, millions years of being intelligent might unavoidably lead to unforeseen consequences, like just losing interest in existence, or abandoning simple minded and boring goals like expending and colonising or grand and vain attempts at ruling or making a mess of a whole galaxy. I know, it suffices of only few species/subcultures escaping such determinism, or only one successful attempt at building an immortal semi-intelligent entity unable to change its silly goals to ruin this explication, but yet. Goal driven and causality seeking intelligence might be a very limited interval on "complexity scale" (for lack of better measuring stick).

Obviously, most simple explanation is just we are alone of our kind on a possibly very large spatio-temporal span. All other explanation seems more contrived. It would just leave us with the question of why intelligence is so rare, which could be answered like "because it requires cosmologically incredibly improbable chains of events", nailing down drake equations right terms to near 0 (even while the more mundane planetary left terms appeared more promising).

Thank for mentioning the SETI talk Standing Space. Quite exciting. I like the idea of "something obvious for ANY advanced technological society, but not yet discovered by us". As we are approaching the technological level of being really "space faring", that would imply major discovery is not far. What if leaving baryonic matter to live in the dark sector is just the way to go ? ETIs could be traversing us right now ! Not implying this is THE explication to the Fermi paradox (again, less contrived explication is "just nobody is out there") but the reality might be as crazy as that or more : parallel "phased out" universes, whimsical mathematical transcendence of hive consciousness, whatever. But the possibility of invasive species/artifacts left over before such transition makes it hard to believe that such transitions are common, hence that just reaching our level is common.

Anyway, nice thoughts, and makes me wonder why we (I mean, at least a lot of space enthusiasts) want so much ETIs to exist and interact with us (in a civilised way hopefully). While many progress still has to be made for us (ahem, humans at large) to fully appreciate and benefit from the diversity of cultures and subcultures within our own kind, and multiculturalism by itself is a certain kind of culture (not identically shared across all cultures), and when we finally learn (if ever, but it's already the case to some extent) to share positively those differences it might be at the cost of less diversity, well I'd like to believe one of the highest drive of intelligence is to meet the others, the strangers, the aliens. Otherwise it's just solipsism.
If this drive is as strong as I feel, almost a prerequisite for conscious life to have some sense at all, then in the absence of ETIs then we will have to invent them. That's already the case as fictional characters but we are probably just projecting our own mental grids (extremely wise, extremely bad...). The value of a true encounter of the third type is just : extremely not human, and that seems impossible to imagine/design by a human, even if some SF writers did/do some wonders. So really we should export humanity to as many worlds as possible, so that for better or for worse, when descendants meets again thousands or million years later they could really enjoy their differences. For me it's not a fear but a hope, and light speed limit is a boon because it means life islands with huge spatial and temporal distances between. Recovering a sense of vastness again.

@fribnicat
I'd very much like to introduce the concept of "objective solipsism" (but please help me!)

All your experiencies are impeccably solipsistic.
No one CAN know that you experience anything. Not even your nearest human relative. So forget about ETI relating to anything to which you can relate to. It is not ex-human, it is actually everyday inter-human. Solipsism is the only thing we have, the solipsistic imagination that there exists stuff like ETI or even other humans who have their own solipsism (like your wife/husband/child). It is very inconvenient that this fact doesn't go anywhere, that nothing can be deduced from it, but the fact to accept is that it doesn't. In order to get out of this trap we might need to reconsider basic stuff like logic or the concept of experience. Or maybe just lay back and relax until its over...

That might bring us to the brink of metaphysics, ok for me but not sure it's appropriate on this forum nor if we could be any deeper than serious philosophers (which I'm not).
My take on that (from my own solipsist experience but also some readings and few social interactions) is basically that my existential experience right now is not much more different from that of a lot of other (similarly minded) people on earth than it is from myself at another time in my life (say, yesterday). It's only the time continuity and strong coupling (informationally speaking) with me at a moment and me at another moment that gives a sense of temporally extended self in a relatively well circumscribed spatio-temporal "pipe". But this tube, or the informational patterns in this tube that are me (I'm not above those patterns or "emerging", I is those patterns), have an origin, a biological birth in continuity with 100s million years of ecosystem co-evolution before a much more recent split, making all human animals my fellows. And more importantly my intelligence and mind, while I live it as mine, is in fact deeply rooted in a culture of countless thoughts thought before me or while I was growing and learning. Without society I would be nothing, my thoughts are (not necessarily coherent) fragments of (a part of) a whole species. If informational coupling is what can give myself a true sentient identity, then I don't see how weaker but omnipresent coupling with others could be a less authentic way for a part of space-time to know, and would I dare feel, another part of space-time.

At least assuming I'm not a Boltzmann brain imagining a whole coherent life with others while I'm in fact just a random fluctuation in a decayed thermal bath (which following some anthropic reasoning is cosmologically more likely than a whole observable Universe for just a few billion real humans). But that's not interesting, as right now I would only be falsely arguing with myself.

So to follow a pragmatic and naturalistic approach to these delicate matters, I would conclude that there is nothing magic in a part of a brain being signalled by another part of the same brain by ion channels modulations compared to a brain signalling another brain through speech. Bandwidth is not the same therefore the feeling of a "gap" between individuals, but recurring coupled dynamics would indicate the same "phenomena" or rather organisation : I do really feel what others feel, if in any sense feeling is relevant.

I'm not recurring much coupled signals with aliens these days so I would say that I'm not feeling the existence of aliens, but I'm expecting that this "mechanism" of empathy (not necessarily sympathy) through signal coupling would be relatively universal. Call it a higher scale or "second order" form of consciousness, collective consciousness and the knowing of intelligence when we see it, interact with it, aggregate to it, though loosely and with "self" contradictions, more like a subconscious chaos (might look into Jungian works there).

Okay, first sorry I didn't reply before, just picking up on a couple of the things you say.

First yes interesting point, that people want to meet ETIs, but at the same time have a fair amount of trouble getting along with other humans, with just slightly different cultures - at least as must seem to ETIs.

Would we really find them interesting or learn from them if we did meet them, or just find them plain weird and most people be prejudiced against them because they have ideas we find hard to understand?

Is that what you were saying? If so I can see the point, not sure if it would be like that but can see how it could be an issue.

With humans spreading through the galaxy - yes - it's a nice thought that it could just be a positive thing, that through spreading the humans become interestingly different, that though we might not meet ETs, we could meet almost alien far distant human cousins, maybe adapted to strange worlds and transformed in many ways..

Yes plus side, if you could make sure it works well, is that the galaxy gets filled with interestingly different descendants of ourselves in a rich cosmopolitan, and wonderful society which is basically in harmony, doesn't cause damage, respects ETIs that are different from ourselves if we encounter them - and returns to Earth with new discoveries and ideas.

Could happen. It could be wonderful if we can make sure it works out like that, indeed.

But - how can we make sure that does happen? Given the many million trillion colonists there would be in the galaxy by then. They would certainly be able to make Stanford Toruses or similar from asteroids and comets by then. So, trillions in each solar system, and several hundred billion stars in our galaxy, huge numbers of colonists - and - seems you just need one rogue element out of all of those to spoil things? Not even malicious, just someone who does something stupid with the ridiculously powerful self reproducing technology we would surely have by now.

As for solipsism - well - just a few thoughts. I did study philosophy actually myself as a second degree, undergraduate level.

I'm not sure though where this comes from, but a few thoughts that might be of intereste.

First, who is the solipsist, and who are the illusionary everyone else who don't really exist.

Is it you or is it me who is real?

Or neither of us, some third person maybe someone we only know slightly or have never met?

You might think it's obvious, has to be you - but - what are you exactly? Where do you begin and end...

As with Descartes, you can start with yourself, but following up connections, and soon you find you end up with the whole universe has to be real.

We are made up of these connections with other people, and the things around us. And through that, then in a way we touch the whole universe, and the whole universe touches us.

It's not so easy to split off a little bit and say, this bit of the universe is me, and is the real thing, and everything else is illusory.

So, it's not easy being a philosophical solipsist, I think. I don't know of a major philosopher who took the point of view (do correct me if you know of one).

It's perhaps a bit easier to be a nihilist and say nothing exists at all, because then you don't have to make this distinction between the thing that's real - yourself - and everything else which you think of as unreal.

But - nihilism is also rather hard to accept because, if there really is nothing at all, then where does - e.g. this comment I'm typing just now, or the room around me, computer screen etc - if that doesn't exist - what can that mean? Why even ask any questions. Who is asking the questions if nothing exists.

Sounds like most info and logical arguments to do with ET has been covered intelligently here, but I have a few things to add. I agree with the idea that ET always following a "transcendent" path and leaving no evidence is unlikely. Here is my thought process:Firstly starting from pure logic yes/no either we are special or we aren't.

1. We are special and there is and has been no other space faring intelligent life in the galaxy. I find this pretty believable but impossible to be certain about. I think the most likely places for the "great filter" are no life to life and single celled life to multi-celled life. I in fact favor single cell to multi-celled as being the most likely. That "boring billion" etc has to be significant. As far as I am aware mitochondria came about from a chance meeting of two cells. Evolution doesn't normally work like that and it could be something with a half life of say a trillion trillion years rather than a result of a continuous process. This solves the fermi problem if true.

2. We are not special. Now this means that intelligent space faring life is common and has been. Of the 100 billion stars then say 1 million have produced intelligent potentially space faring life. I will start by clearing up what I see as a statistical/logical error here. The argument "they are not like us therefore we have not seen them" Well why not?!! What would stop at least some of such a huge number being sufficiently similar to want to expand etc. That potential explanation actually makes things worse not better as you have nothing then to explain our difference to the other 1M civilizations. It would make us very special and in a way not explainable by anything understandable like single cell to multi cell.

It can be at most a tiny part of the drake equation or great filter.

2.1 So now assume that we are not special and we are here because *all* civilization follow the exact same course and go all Zen before expanding. Like other people I find this pretty unlikely. I think its safe to assume that to lose the desire to expand we would have to evolve into something pretty much not human anymore. So we need to go AI/singularity etc before we develop the ability to make those Replicators. Now what would influence the relative speed of those two things? Space travel vs making consciousness in silicon/graphene etc. For this to be the answer it has to apply even to the most extreme 1 in a million place where things don't go that way at all. Lets imagine how things could go differently.

The intelligent life form is more like the size of an elephant with a bigger brain than a human (I think there was little to stop the elephant from becoming tech, just the trunk not being able to manipulate objects well enough rather than brain size. Similar for dolphins, being in the sea without hands stopped them not brain structure). Now this does two things. Firstly they have a lot of spare brain capacity above being conscious so they can do things like calculate like an autistic savant easily and everyone can do it. Hence little immediate need for computers. Secondly I consider the best way to AI is by brain uploading/copying we don't understand how to program intelligence, but do know how to copy it. A larger brain makes it harder. We don't know the minimum size for consciousness and probably won't start there, instead start with a digital copy of a human brain. Similarly for the aliens but the threshold to cross requires better AI/brain mapping tech because their brain is larger and they don't know what parts are the essential ones. Now further imagine there is no easily accessible silicon on the planet. So no need, no capability and a greater threshold to get to conscious AI. It is also easy to imagine that they have similar sustainability problems to us, but are surrounded by nice asteroids that need mining. Well getting people into space is difficult so the obvious thing is to make a self-replicator to send the materials back to their planet. Perhaps they use silicon from asteroids now to help with the AI. It seems pretty clear to me in this case that the Replicators would be made significantly sooner than the conscious AI as the AI required for replicators is much less. Well it would only take one to be let loose... A civilization fighting for its survival wouldn't care about accidentally letting some lose. I don't think you can depend on them realizing the importance of such a thing.

Also you can make a VNR that is pretty safe if it could only land on small asteroids and wasn't programmed to evolve it would never be able to land and take off again on planets so couldn't trash the galaxy only re-arrange asteroids. Light sail tech but no rockets etc on replicators would be safe. Such a galaxy we could still exist in. We would just find it mysterious that there were no asteroids anywhere in our solar system or others. However we do observe easily mine-able asteroids.I count that as pretty strong evidence against this scenario, 2.1.

2.2 We are not special and enforced non-interference.In this case one of the first space faring life-forms expanded across the galaxy and left no mark except to stop others from destroying each other. Their presence could be simply replicators that hide in the outskirts of every solar system and destroy other replicators, it could be an enforced prime directive like thing where if we go and try to destroy another planet they stop us with some robo-cop that is built to be stable forever and never get bored. And finally there is the dark explanation that is known but not mentioned where the first civilization turns into a mad scientist single minded observer of new civilization and wipes them out when they try to colonize other stars because it wrecks their other observations.

You just can't decide between 1 and 2.2 logically, however 2.2 sounds contrived to me.

Getting into the speculation more, if you assume some kind of multiverse and that the first civilization always takes over their universe, then that would make us likely to reside in a universe where life is very unlikely and hard to get started. In the universes where it is likely it would evolve soon after the big bang and we wouldn't reside in it to observe 13.7 billion years etc.

FINDING OUTFinally how do we find out? Well the James web space telescope will tell us a bit when we measure atmospheres of exo-planets. If we find 1000 planets in the habitable zone, but none with earthlike atmospheres then we have some confidence that life isn't common. If we do find life traces in the atmosphere it doesn't tell us much because the filter could be from single-multi cell. If we really want to find out the answer, then we can rule out 2.1 and reveal it to be false by ... making a safe replicator that can only eat small asteroids, can't evolve and letting it lose. Tempting isn't it !! haha.

If it is allowed to reach other solar systems and eat all the small asteroids, then (1) is the answer and we are alone. If it is stopped, then 2.2 is the answer. If we start discussing such a thing then decide its a childish thing to do, then we are really none the wiser as to whether all civilizations follow that course. Likewise if we find simple life on say 100 other worlds and attempt to disrupt it by sending our life there then its the same. If no-one stops us we are alone because by symmetry earth would have simple life once and if life was common and allowed to destroy each other we wouldn't have lasted long enough to exist now.

(Add simulation hypothesis to Boltzmann brain problem to make things even more confused ... we are being simulated by the first civilization, it has taken over the galaxy and is having fun confusing us with our existence)

PERHAPS WE ARE FIRST TECHNOLOGICAL ETI IN OUR GALAXY, EVEN IN THE UNIVERSE

Yes, on the 1. then - I actually think that's quite possible. Yes developing multicellular life - something must have been going on for that billion or more years.

Also though - the evolution to the first cells. I think when you look at the complexity of even the simplest DNA based cells, it's at least possible that there was too much evolution needed for it all to happen in our solar system. Perhaps it happened on an earlier orange dwarf, or red dwarf - far more numerous stars, and also likely places for life to start. Then perhaps one of them passed through our solar system as it was forming or during the late heavy bombardment, when it would be easy, with all the giant impacts, for life to transfer to one or more of our planets.

"Scientists have looked at evolution on Earth, and nearly everything happens so quickly on the geological timescale. It's now thought that there was life on Earth already within a few hundred million years of its formation, and quite probably almost straight away. So, the way this is usually interpreted is that it must be really easy for life to evolve. Also there were many other steps along evolution to humans, and again these steps, most of them, happened quickly enough so that they seem reasonably easy too.

However, now let's turn this idea on its head. What if it is really hard for life to evolve at all and typically takes billions of years. Suppose there are ten different steps like that along the line to evolution of humans and each one typically takes billions of years. In that situation, most civilizations will not arise until tens of billions of years in the future, but there has to be a first civilization. In that first civilization, then all the steps would get completed, just by chance, within a period of say 5 billion years. Now look at the time line for that civilization. You find that the most likely thing to happen is that the steps are all evenly spaced and each one takes quite a short time.

So if we are the first technological ET in our galaxy, we would expect to see a geological past with everything happening very quickly. So, this doesn't by itself prove that life can get started really easily.

In this situation the first civilization in the galaxy is a rather lonely one as it gets underway typically billions of years before everyone else. Perhaps the reason there are no colonists here yet is because we are first?

SAFE VON NEUMANN REPLICATORS

Oh I'm sure we can make safe replicators and may do so soon. There's one easy way to do it, which is to notice that with exponential population increase, you don't need many generations. Say 8 generations, each generation limited to make 1000 machines and then stop - with a kind of "telomare" that counts down for each one from 8 down to 1 and when you get to 0 it stops

That's 1024 machines in total, enough for more than a trillion machines around each and every single star in the galaxy. Or - just do 4 generations and you get 1012 machines, enough to have one of them around every star in our galaxy.

It would need to be stupendously reliable, you are creating 10^24 machines after all and none of them can go rogue.

But only 8 generations, and - e.g. some strong encryption - not designed to evolve to be better with each generation - and some feedback to check to see if there have been any changes at all not fitting with the plans, if so self destructs.

Would build up to that level of reliability, first e.g. machines with only say 2 generations, to create a million satellites to beam energy back to Earth from a single VNM parent machine. They then stop reproducing after 6 generations.

Also I'd design in a "stop signal". Or rather a "keep going signal". Every year they have to check for a radio signal from Earth - propogated through intermediate VNM - and designed with strong encryption with no chance at all of another ET generating it or another VNM. Signal keeps changing and they can unencrypt it but not encrypt it.

Then - they can only reproduce if they continue to receive that signal. Or even - that they all self destruct within a set period of years if they don't get the signal.

Those ideas can probably be improved on. But indeed, "stay at home" ETIs could explore the galaxy safely with VNMs like this. And we could also in the future. If so, maybe we will find these VNMs in our solar system at some point. And if we don't - I suppose that's a bit of a mystery.

Okay you can say they aren't here themselves because of colonization concerns, what they might do to the galaxy. But - is it that hard to make a safe VNM to explore the galaxy? Maybe they are here, and only make one VNM per star or not that many and we are yet to find it, or it's hidden as in 2001 a Space Odyssey?

But - I think we could be the first. At least first technological. Since, at least by our solar system, there are so many more icy moons than terrestrial type planets, and judging by our solar system again, many of them have subsurface oceans, some at least with good possible sources of energy - like Europa with its oxygen - maybe most ETIs evolve in those - and that's not too easy an environment to evolve technology - that could be an example of a galaxy with many ETIs but hardly any technological ETIs. Plus in our own world, many intelligent animals like parrots, dolphins, elephants indeed, etc, who might have a great deal of difficulty constructing technological machines if they evolved the intelligence to do so.

Yes exciting times in near future should have a good idea of the atmospheres of many nearby exoplanets - and then - can start to see if there is evidence of life on them. Might help answer some of these questions.

Also megatechnology - truly large scale technology we'd spot even in other galaxies. You'd think a civilization that does colonize a galaxy would start doing that sort of thing within a few million years - either deliberately or accidentally, and result might be obvious even from millions of lightyears away as our telescopes improve. E.g. if someone has unleashed a paperclip event horizon, we might spot a galaxy made of paperclips in our telescopes :). (Well :( if you are an ETI in that galaxy or was).

Yes that log genome vs time graph is interested, I heard about that but forgot to mention it. If true it would also explain a lot as our ancestors would perhaps somehow have to have evolved a bit on an earlier solar system and survived interstellar space. However though I think the probability of skipping the earliest steps is unknown and may not be high. You cant randomly get a complex cell from nothing but chance could have sped up the earlier transitions. Still if its a 1 in a trillion chance that had to happen on earth then that explains a lot.

Yes, is all guesses now. Big unknown in that log plot is - that in all the region they plotted then it was all DNA right the way through and basically modern cell mechanism - but that's far too complex for the early cells - so did they evolve at same speed with simpler cell mechanism. Or could the simpler cells evolve more quickly to higher complexity (or more slowly because they hadn't yet got the modern cell mechanism for error correction etc). We might find answers there with organics from the early solar system preserved on Mars or meteorite impacts on the Moon etc.

Solipsism is the obvious. You don't exist. I don't exist. It is only the phenomenon in themselves which exist. That which is experienced. The thought that there exists something which experience something, that thought is just another phenomenon which exists. The phenomenon of thought has no different status than does the sensation of color or of pain. (I would've use the term "sensation" isntead of phenomenon, but sensation implies the existense of a sense and of something to sense, that is way beyond solipsism).

The nihilist is wrong. The phenomena experienced exist irrefutably. If they are a dream or a sensation of some "real" object or something else or nothing else, is nothing which solipsism cares about. The experienced phenomena exists either way. That is obvious and irrefutable. Solipsism is the stopping point beyond which the skeptic cannot go. That is the constructive part of solipsism.

It was interesting that you earlier mentioned phenomena such as conciousness, emotions, intelligence. Aliens might have other such categories, the connection of which to objective matter (if any) is today completely unknown.

Oh, that's not solipsism. That's phenomenomalism or Existentialism. Yes that's a common view amongst philosophers. By no means the only one or obvious though, or all philosophers would be phenomenomalists.

Yes would be interesting to know what philosophical ideas ETIs have. Do we all end up with similar range of ideas, or are we perhaps influenced more than we realise by our history, the world we live in and our physical forms. Would even a parrot or octopus, evolving far enough to have philosophical ideas, come up with similar ideas to us?

This is a very long post, with hopefully well articulated ideas but widely speculative ever for me. Hope this is not inappropriate.

Foreword @ Standing Space. I mentioned "solipsism" to qualify the state of a species like human that would not as a whole find any other intelligent species of different origin and history but that could rather be stated as just "terribly feeling alone". I have not much to add to my views on solipsism on an individual basis. I would agree that what matters is not what It is (ontological dissertations) but what it does : at the end of the day it makes no difference, so I assume I exist, other humans exist to the same extent, and a multiplicity of entities exist on their own and interact at different spatio-temporal and complexity scales to make somehow a "reality network" that is as real as reality can get (even if sometimes a bit fuzzy when looking very very close).

As for the pragmatics of "feeling alone" and the need to find some answers/echoes from an intelligible otherness, I would trace that back to the early religions, spirits, ghosts, angels... sociologically our drive and longing for ETIs can probably analysed in the same terms. But that should not necessarily discredit the legitimacy of this search, and the progress we can make by approaching that goal with a rational mind. Because should it lead to successful contact, and that would be by very rational and technological means, shaking hands (pseudopodia...) or even just recording a few bytes of actual aliens would be a shattering revelation to mankind. It wouldn't necessarily end all attempts to see theological meaning where there is none but would help to relativize...

And even if it fails because we would indeed be alone of our kinds in a purposeless materialistic reality, as I stated, if ETIs don't exist then we should invent them, like we did of the angels but with more interesting results in terms of otherness. What an alien can bring to us is his "extreme non humanity" but on the other hand there is probably more humanity in any form of intelligence than in a piece of earth rock. So we are looking to the otherness in the "same of kind", like we get used to as individual in a social species with a sense of individuality. It's a subtle play between similarities and differences.

Most individual engage their intelligence (rationality, emotions, creativity...) with other individuals more than on rocks or meteorites. Not every geologist or crystal collector is autistic, there's still a lot of legitimacy to develop a strong relationship to stones and their mysteries but it's only natural that we spend much of our times interacting (closely or more abstractly through books) with other humans. Sorry for the long and impromptu style of this, closing the gap to the original thread soon. Simply put : an earthly human is more "interesting" and more fun to interact with than an alien rock to most people, including space enthusiasts. And the only alien reality so far is rocks, and gas, and plasma, and other entities with no obvious "purpose" or agenda of their own.

Now what DOES intelligence ? Basically it helps to survive. It has the ability to close a gap between a given situation and a wanted outcome (life, reproduction, safety, comfort) by understanding of self/environment system causality and by subtle manipulations of those causalities rather than by brute force. Intelligence is an economy of energy, like when an autotrophic bacteria "decides" to move against a small gradient now, rather than just go with the flow and invest more ATP into ion pumps when the situation goes deadly later on. This knowledge of the self/environment can be "hard coded" into DNA, or learned by trial/error at individual level, or learned by parents or by reading the knowledge of a culture. At some point or another knowledge is gained through trial and error processes. And it is based on a perception of causality. Any intelligent species might "see" more causality than there is really because it tries so hard to find connections. Now rationality comes into play as we get more leisure time, time to think beyond the next meal, and we get interested into our own causalities, and we acquire better skills at modelling dynamical systems at large, even while dreaming situation that don't exist but just could. That's not necessarily by writing down equations. A dog can predict the trajectory of a free falling ball with ease, bouncing comes at a surprise at first but then quickly gets integrated in the model. That's the "got it" or Eureka moment of the dog. How sad would be the world if we couldn't share some insights with animals. There is some degree of universality and "same of kindness" in naturally occurring intelligence when it comes to this ability to integrate dynamical systems models and internally "replaying" them or I would say feel or "co-feel" them. This I would hypothesize would be common to all forms of intelligence, including ETIs.

There I should mention some reference, for those interested in these lines of thought (or streams of consciousness) of recurrent signalling and structural/model coupling : The cybernetic brain by Andrew Pickering (univ. Chicago press) while rather a historical account on early British cybernetics movement (G. Walter, R. Ashby ...) does a great job toward "sketches of another future" (subtitle) where intelligence is less seen as a matter of logic but more of interplay and co-evolution. Might also be of relevance to the topic a shorter text by Pickering about transhumanism and its shortfalls (to be fair, not all transhumanists share the criticised biases) : "we have to expect new selves to be continually bubbling up in our dealings with the material world, even dealings that aim to hold the self constant" (citation chosen by me)

Back to the topic : if this analysis holds then human intelligence is this "model building" or "dynamical system mirroring" capacity developed to such an extent that we can now model ourselves (sense of self) and our own relations to the world : rationality as a way not only to model the world but also to model ourselves as a part of the world, and to model our models as part of the self/world system, therefore being able to somehow change our views on how we change our views. Intelligence of an epistemological level, my cat would only yawn at that one. We are getting farther from the intelligence seen as the functional smart way to save metabolic energy in a recurring pattern of self preservation. And yet it's hard to see how any technological intelligent species could skip that one aspect of intelligence. Biological then sociological natural history is chaotic and full of contingencies, not a set of convergent roads, but some universal "aspects" should appear one way or another if progress toward more ... more complexity is to proceed. Like active exchange of matter/entropy with surrounding (breathing or such), active circulation of metabolic fluids (like pumping blood) etc... and why not up to epistemology ? Admittedly this looks like a very linear perspective on evolution, as if there was only one way of being "more complex" or "more evolved". It's not "only one way", but would be multiple pre-requisites.

I wont go much into the infinite regression territory of "how could a model of a system that holds models fit in the holding system itself", lets say that our model of self is smaller (and therefore always an approximation) of the real self, or it is somehow "compressed". But I would like to risk that transcendence, seen as a possible decoupling of a pattern from its substrate, is present as soon as any language exist, counting DNA coding as a language at one end, and written books and recorded musics at the other : soul/body duality concerns would be part of any Intelligent species history, one way or another. Can't tell how it could be overcome. Precisely the kind of topic we would love to chatter about with some Others.

So in the end, aliens (of similar degree of evolution) could be very similar in mental aspects. Unless it is an intrinsic limitation of our biological common lineage, all organisms we recognize almost as highly evolved as us (by behaviours, not only by shape) have a centralized nervous system, connected to nearby eyes, a bilateral symmetry, are highly mobile (not plants) with a high number of degrees of freedom... The octopus, the chimp, the spider (lot of eyes, surprise, but two major frontal).

But if aliens wont show up we are still left with a strong sense of cosmic loneliness. And instead of asking "what can we do together of the galaxy" we are just left wondering what can we do alone (as a species) in a galaxy. Consider we continue to be intelligent, refining our aptitudes at closing any gap between a present state and any wished state by our understanding of causal relations in reality. That means : we can do anything physically possible. Say, turn 20% of stars in milky way into synchronised pulsars (that should be seen from quite a way). Think about it, instruct our super AI computer of this goal, let it figure out how to do it (and make us immortal so we can see the result).

What do we do when we are a space faring species, when everything becomes possible, when we are no longer acting by necessity or habit or frustration ? Rationality has not much to say about that. The next aptitude would not be to solve problems but to make problems. Artificial problems. Interesting problems. That's actually the activity of mathematicians and philosophers and musicians and artists and more and more of politicians. I'm including politics because we see decisions seemingly to just occupy the crowds with sometime senseless activities (like filling car parks with cars nobody can/want/need to buy). Its ironic that while we are at a techno-industrial energy transition period that gives this illusion that energy is scarce (and getting scarcer, at least under the form we used to know) the real long term problem is that of an excess of energy. Meanwhile we never quite reached a satisfying level of wealth redistribution (in case you wonder, I'm somehow leftist) and it gets worse when crossing such energy crisis which would require some serious and rational problem solving. Not throwing the stone at the politics, short of a totalitarian hive mind history remains chaotic and it's hard to aggregate efficiently a limited amount of good wills in a sea of billion individualities (religions and dogmas do try). But the urge to dissipate excess energy will be felt very strongly when (if) a self sustaining space economy can emerge and basic survival problems are overcome. Then the "next level" of intelligence, the "high ground" would be the capacity to generate artificial activity : problem making. I suggest that one of the interesting problem to tackle is to find ETIs, and short of that to make them, rationally so that they are not becoming angels. But I wouldn't try to enforce that as the only problem that could constructively occupy human descendants : levels of complexity and structure are limitless, let every one dissipate energy as he sees fit. A few solar systems might get fried in the process, maybe the whole galaxy sterilized by accident or on purpose (it's a risk but by that times some intergalactic seeds would probably have reached further destinations), some peacefully minded tribes might have to learn some basic mitigating skills to manage annoying dogmatic galactic enforcers, but overall it should be exciting times for life.

References :
- Making aliens in "permutation city" by Greg Egan
- The problem of dissipating excess energy in "The Accursed Share" by Georges Bataille
A quote from wikipedia's entry for the later :
" I will simply state, without waiting further, that the extension of economic growth itself requires the overturning of economic principles—the overturning of the ethics that grounds them. Changing from the perspectives of restrictive economy to those of general economy actually accomplishes a Copernican transformation: a reversal of thinking—and of ethics. If a part of wealth (subject to a rough estimate) is doomed to destruction or at least to unproductive use without any possible profit, it is logical, even inescapable, to surrender commodities without return. "

Another thing to maybe add to the list would be fission nuclear thermal rockets. Nuclear thermal rockets were very successfully tested on the ground during the 1960s and 70s, and then again during the SDI in the 1980s. We could build such rocket engines today.

They seem to be great for trips to the outer planets, but too limited for any interstellar travel useful to us who are alive today. And one intermediate semi-insterstellar target which might well be achievable within our lifetime would be a (radio) telescope in the focus of the Sun's gravitational lens 700 or 1000 AU away. From there we could in great detail examine the atmospheres of nearby exoplanets (though only one target per such telescope is possible since it can only look pass the Sun and cannot be "turned").

Nuclear thermal rockets would make mining of rocket fuel on the Moon or asteroids redundant, although water and building materials would still be attractive. The main drawback is that nuclear thermal rockets won't at all lower launch costs from Earth since they cannot be started on the ground for environmental reasons. They need to be supplemented some completely different launch technology.

I'd like to add to my own comment, that even though I think that environmentalists generally overstate the threat from nuclear energy in all forms, my understanding is that fission nuclear thermal rockets launching from Earth would spread an amount of radioactive hazard which would be unacceptable even to me, if done at any useful scale.

Conventional rockets carrying nuclear thermal engines, to be activated away from even LEO to avoid the possibility of them returning to Earth, should maybe be launched from West Sahara. A failed launch would then cause a crash on one of the least populated parts of Earth in an environment which should be relatively easy to decontaminate by having bulldozers transported to the crash site to scoop up the surface sand and safely burrying it somewhere. If the ten largest and most exposed cities in the region were equiped with shelters (buildings which could be used as everyday hospitals and schools), and airlifted decontamination and evacuation capabilities were ready to deal with a launch failure, I think that even the worst case risk could be managed very economically. Only four (4) million humans live in Sahara, most of whom live far away along the Nile in eastern most Africa. The GDP of the state of West Sahara is about one (1) billion dollar a year. The population would greatly benefit from the investments in infrastructure in their region which a space port there would provide.

Now, with this comment I'm maybe more "feet on the ground" than Robert Walker intended to discuss here. But I like the practical combination of (half) proven SpaceX Earth-to-LEO technology with the (half) proven use of fission nuclear thermal rockets. Then we won't need much of the more speculative space mining or solar harvesting type technologies:
- No need to harvest fuels in space.
- No need to harvest solar energy in space.

Okay thanks, yes that deserves a mention, wasn't aware of the nuclear thermal rocket. Never actually flown but extensively studied from 1955 through to 1972, with large scale tests as well.

Seems from the Wikipedia article, it's a nuclear reactor, which heats the hydrogen. So instead of combustion of hydrogen with oxygen, you simply heat it up by putting it through the nuclear reactor - and surprisingly even with the extra weight of the reactor - that gives more thrust for less weight. And - if the reactor stays intact - then it's reasonably clean, only exhaust is pure hydrogen.

Though - obvious safety considerations, sending a nuclear reactor on a rocket into space. I thinkif I was a resident of Morocco say, I wouldn't be too keen to have these flying into space close by to me, no matter what the financial incentives and safety assurances, and wouldn't be too reassuring to be told that there are radation shelters in all the big cities that I can retreat to in the event of an accident.

However, the Japanese did discover Uranium on the Moon a few years back. Perhaps that means some time in the future we can create these in space. Similarly also the Orion fusion pulse rockets - hard to see them safely taking off from Earth but easier to see them part of some future space industry.

Anyway whatever - yes it is worth a mention. Not so dramatic as the other ideas, only a factor of 2 improvement, but significant all the same.

If you actually were one of the 500 000 inhabitants at the coast of the state of Western Sahara (not Morocco too far north) who try to live off $2500 a year, then you might think differently about that useless desert to the east of where they live, compared to the money and infrastructure you would gain by GDP-doubling space port investments.

Besides, the launch crash rate today is about 2%. A launch abort system could be applied as with crewed launches. And the nuclear material would be capsulated so that it lands in one spot where it could trivialy be picked up without any health hazards. It's just easier to do over Sahara than over an ocean. And since practically noone live in that hell, it's an extra safety measure too. "Shelter" would simply be an overpressurized tent to protect from inhalation of alpha particles, if an oasis at the time visited by 100 bedouins extremely unlikely happened to be hit by a crashing engine. Two plutonium RTGs have already crashed from space into the oceans without any trace of environmental impact. One from Apollo 13, the other was recovered from the bottom of the ocean and reused in another satellite(!)

Nuclear thermal propulsion is available today and meets all propulsion needs in the Solar system. It needs to be complemented by an Earth-to-orbit system to launch them (of which you list many) and by non-fuel ISRU on moons or asteroids.

Oh a Plutonium RTG is different - that's well encapsulated and just using the heat of the decay to generate electricity. I'm not too bothered by them, can believe they can be made safe.

But here you are talking about a working nuclear reactor with circulating fluids. I'd need a lot of assurance and testing to be happy with one of those crashing near me. Yes the deserts are almost uninhabited but that's not the same as nobody there.

Remember, it's not just one of these, but thousands, maybe eventually millions every year on the sort of scale you might get in the future if it's as common as passenger flight.

Also - yes it's a step towards cheaper space flight - but not such a game changer as, say, the Skylon would be or the JP Aerospace or the maglev or some of the other ideas here. Halving costs to space, perhaps, but not reducing it to just dollars per ton.

I can see it as being part of the mix, but probably needs more work to improve safety for launch to orbit - or else sourcing the Uranium outside of the Earth.

BTW searched a bit more about uranium on the Moon - it is there - but not in quantities useful for mining, similar to levels in granite, at least the deposits found so far.

A non-activated nuclear thermal rocket engine launched as payload from Earth is just a high density clump of perforated metal. It would fall down in one piece even if its chemical carrying stage exploded and the abort system failed. Every bullet is an explosion next to a lead payload. Uranium has about the same density as lead. Lead bullets don't spray all over the place, they simply land on a spot. Even if the aiming failed.

Governments have detonated 1000+ nuclear warheads in the atmosphere/oceans. As I propose it for geographic and demographic reasons, it would also save the lives of thousands of the few extremely poor nomads who still try to survive in the Sahara, by industrilizing their habitat.

An even better thermal nuclear rocket engine type proposed by NASA is the FFRE, Fission Fragment Reaction Engine. Instead of using the radioactive heavy metal to heat some carried reaction mass, the fissured parts of the metal fuel itself would be used as reaction mass, and then being magnetically directed since it would be ionized:https://space.stackexchange.com/questions/2364/are-nuclear-powered-engin...

Even otherwise, I think that the fission thermal nuclear engine is complementary to mining water (and hydrolyting it) from Lunar poles for reaction mass. No environmental concerns over there. An outer or heavy mass Solar system space transportation system within grasp in our time:
A) Earth-to-LEO shipping of nunclear engines with reusable chemical rockets.
B) Moon-to-space shipping of reaction mass in the shape of (the hydrogen from) water. And of some construction materials.

1. Elon Musk is a bright guy with access (recently) to all the scientific talent he needs. So that brings the question: why does he still talk about colonizing Mars? Is he (despite all) unaware of the radiation and crash-landing issues you describe? Or does he dispute your analysis? Or have much greater faith in the emergence of engineering solutions to these and other obstacles? Or is all his talk about Mars some sort of enormous hustle?
2. Regarding the Space Treaty, your article reads as though you think that is likely to be honored once real business or political conflicts emerge. Or perhaps you are just recommending it be observed? I think the "physical laws of politics" to coin a phrase, are not likely to change. Treaties between sovereigns are observed to the extent they continue to be to the advantage of the parties (where "advantage" includes a calculation of the cost of conflict with other parties.) I do, however, think that the environment that determines politics once we leave Earth will be very different, at least for a while. More like the era immediately after the discovery of the "New World" in some respects, both because of the distances (and time lags) involved and because of the vast amount of unclaimed (and therefore disputable) territory. It's likely to be "interesting times."
3. A previous comment noted that the speed of light may explain why we haven't heard from other civilizations. I suppose one might even say that the lack of contact is a bit of evidence that the speed of light is an insurmountable barrier. Another explanation (which I believe you mentioned in response to a comment here) is that we may simply be of no interest to a very advanced civilization: not a threat; not possessing significant resources, and not relevant culturally to a very different type of sentient race (very likely to be completely physically machine if you follow Kurzweil.)

ELON MUSK AND OTHER MARS COLONIZATION ENTHUSIASTS

I really don't know about the colonization enthusiasts - it's Robert Zubrin as well - he's got a lot of influence and is a good engineer and scientist. And he has given vigorously argued reasons why he thinks that it won't matter at all to introduce Earth life to Mars. Not many people agree with him there, amongst those who specialize in these things. But he believes his own arguments, I think.

So, might be that they find these ideas totally convincing, and expect to find life on Mars which is identical to the Earth life in the same habitats, find Antarctic and Atacama desert habitats on Mars that are just identical, same microbes and everything, seems to be what Robert Zubrin is implying though he doesn't spell it out like that.

With planetary protection, then they might be thinking of the idea of an end of planetary protection - that's been built in from the start, that there would be 50 years of exploration and then you start colonizing. But that then got extended, because we've done hardly any exploration compared with what they expected - and then you now get people saying we might want to keep Mars pristine indefinitely, so it's no longer clear there will be a definite end date when it's thought that all the necessary biological exploration is already done and it doesn't matter if the planet is contaminated.

So - in the planetary protection publications you have these two things at once, that they talk about need for higher standards of protection, but still have this idea also - of a future phase when the protection is no longer needed, or doesn't need to be so strict. But no explanation of how you get from one to the other, no kind of future plan for it. So, those really keen on colonization could tell themselves that this will all get sorted out within 20 years say, the scientists will have done all the research they need on pristine Mars and it will be all go for colonization.

That's the only answer I've got. In case of Elon Musk is just speculation as he hasn't talked about it as far as I know. Perhaps he has thought all this through, or perhaps not given it much thought, I've no idea.

With Robert Zubrin, he has talked about it a lot and has convinced many by his arguments, but he must know that his ideas on this subject are not universally or indeed even widely accepted in the planetary protection community of scientists. But no idea how he thinks that will play out.

SPACE TREATY

2. With the space treaty - well I think it's like the Antarctica treaty - that space really isn't of that much interest for colonization. Though could be for mining indeed, and solar power. But not as a good place to live.

So, is not going to be any point in staking out territories, really, when it comes to it, there's nothing worth staking out. Anywhere on the Moon is pretty much like anywhere else as a place to build habitats. What matter are the habitats and who owns those, because those are going to be the only places worth living in space. Except that is for special resources. E.g. caves on the Moon might be an issue because - there aren't that many natural caves. And water ice at the poles, that might be a big issue, what happens there.

So - I don't know the answers - but there are plenty of resources in the NEOs, you don't really need to use the scarce water ice at the poles of the Moon for instance, if it does turn out to be scarce. At any rate that's where I see reason for hope - that functional ownership, ownership of habitats, and mines, and places that you build yourself and occupy, might be all that is needed in outer space. Even if you build Stanford Torus habitats - well that's a built habitat so whoever built it would own it. So the existing OST would be fine there also. Build a large colony on the Moon with greenhouses etc - as much as you can cover and occupy and grow crops on - then that I think would also be owned by you, under functional ownership, probably with some extra law but basically part of the OST, so no need to renegotiate it which I see as a potential legal nightmare that could probably never be done.

SPEED OF LIGHT AND CIVILIZATIONS

Yes - that could well explain it if they are also not numerous, stay in their own home system and just send explorers through the galaxy. Focused light communications via laser between say a dozen or more ETs and maybe another hundred or thousand or more spaceships roaming our galaxy, say, to take an example - we'd never spot that.

But - if they started colonizing, in exponential fashion, - then it gets hard to see how that would stop before they fill the entire galaxy - and they can do that easily at well sub light speed - in that case the nearest ETIs should be right here in this solar system - unless there was somethig about our solar system that made it utterly inhospitable to them which seems unlikely.

That's why I think myself, that if there are ETIs, they may be explorers, but are unlikely to be exploiters or colonizers.

Thanks, interesting link - idea of civilizations forming a super-organism - not necessarily I think shared consciousness - but just so interconnected that for practical purposes it's a single organism. That got me thinking, about maybe a possible way through the dilemma. If the entire galaxy became a net of super-organism type civilizations - each powerful enough to protect itself against any conceivable threat from individual spaceships or von Neumann machines going out of control - is that a solution?

Or - is there a risk that one of all those super-organisms could still become better than all the others and take over the galaxy for its own obscure ends - basically originally human in origin - but not necessarily humans, could be machines, or biological entities or some hybrid or anything that is simply linked to us by a chain of causation. Makes some technological breakthrough - or just happens to last longer without destroying itself - and finds itself with a few thousand years worth of technology advantage over all the other super-organisms.

It might just move the issue to a higher level of planet or solar system sized entities rather than human sized entities.Kind of like the Borg in Star Trek... But chances are more alien ideas to us and hard to understand than that (even though linked to us via chain of causation) as after all that's limited by human imaginations trying to imagine such things.

Just wanted to add this link to a new book published about Space Elevators from the Earth. Which suggests it may be possible as soon as the 2020s. And may be legal, safe, and practical by then, depending on new technologies that they project would be developed by then, and new materials that they also project would be available by then - detailed study.